The present invention relates to optical fibers and more particularly, the present invention relates to an enhanced mass splice measurement system for testing a plurality of optical fiber splices and also the reliability of the splicer itself.
In present wired telecommunications systems, fiber optic cables have become the standard transmission line through which large quantities of data can be transmitted in the form of infrared light. A standard fiber optic cable is made up of a plurality of individual fibers generally made from multi-component glass, quartz, synthetic resins and/or other material. The individual fibers are generally placed within a plurality of plastic and/or metal tubes. The plurality of plastic or metal tubes may be bundled together and further protected by outer and inner jackets made of metal, plastic, Kevlar, rubber and/or any combination thereof.
Like many other cables, due to manufacturing and/or practical limitations, only limited lengths of fiber optic cable can be placed on a single reel. Accordingly, the fiber optic cable may need to spliced together several times with other fiber optic cables to reach the desired destination. Splicing is accomplished by either fusing or melting two optical fibers together using a fiber optic splicer or, in the alternative, by using a mechanical connection to attach the individual fibers together. Although splicing is preferred, splicing the glass fibers together introduces losses as the light is reflected and/or possibly refracted at the splice points. Accordingly, it is desirable to determine the integrity of the splice and thus, the reliability of the splicer itself (i.e., which optical fiber splicers produce splices with minimum losses at the splice points). Although most modern splicers are able to estimate splice losses, but to accurately determine splicer reliability, actual or true loss is desirable.
FIGS. 1-3 illustrate conventional methods for determining the reliability of fiber optic splicers. FIG. 1 illustrates a conventional method for measuring splice loss and determining splicer reliability utilizing Optical Time Domain Reflectometers (OTDR) 101, 105. As illustrated in FIG. 1, fiber optic cable 102 is spliced with fiber optic cable 104 at splice point 103 using any of the known mass fiber fusion splicers (not shown). In this example, both fiber optic cables are twelve (12) fiber ribbon cables. After the individual fibers are prepared (i.e., outer/inner protective jackets and/or buffer tubes are removed, individual fibers cleaned and cleaved, etc.), pigtails 107, 108 are attached to the ends the individual optical fibers within the cables 102 and 104, respectively. A pigtail can be, for example, a small section of a single optical fiber that includes an optical connector at one end, and can be connected to a single fiber in the cable via a fusion splice or a mechanical connection. After the pigtails 107, 108 are connected to the cables 102, 104, respectively, the connectorized ends of the pigtails 107, 108 are attached one at a time to the OTDR 101. After the first pigtail is connected, the OTDR test on the cables 102, 104 may begin. OTDR 101 launches a plurality of short high-powered light pulse into the optical fibers and receives back scattered and/or reflected light. The received light signal is displayed on an oscilloscope of the OTDR 101 indicating power loss as a function of the length of the fiber optic cable in a graph format. Accordingly, based on the information displayed OTDR""s 101 oscilloscope, the distance of the entire fiber optic cable and light losses can be determined. After the test on the first optical fiber has been completed, the connected pigtail must be disconnected and the next pigtail is connected to the OTDR 101 to test the second optical fiber. Accordingly, to measure loss at the splice point 103 for individual fibers, each optical fiber must be attached to the OTDR via its respective pigtail and tested one at a time. Thus, for a twelve (12) fiber ribbon cable, the above described procedure must be performed twelve times causing this procedure to be highly time consuming. Since, OTDR measurements are direction dependent, it is desirable to perform an OTDR test from both ends of the spliced cable and then average the results to determine the reliability of the optical splicer. The above-described conventional method is disadvantageous because connecting each of the plurality pigtails one at a time to the OTDRs 101 and 105 and performing the OTDR test on each individual fiber from both sides is labor intensive and can be time prohibitive. In addition, loss measurements using OTDRs tend to be less accurate for very long fiber runs. Further, OTDRs commonly require minimum fiber lengths of 50 meters or more making small scale testing impractical. As a general rule, OTDRs tend to be less accurate than other systems using power meters and light sources.
FIG. 2 illustrates another conventional method for measuring the splice loss and determining splicer reliability. As illustrated in FIG. 2, OTDR 101 is connected to a 1:12 (i.e., for example, 1 input and 12 outputs) optical switch 201. Using this method, pigtails 107 connected to fiber optical cable 102 are connected to the outputs of the optical switch 201. Pigtails 108 connected to fiber optic cable 104 are connected to the outputs of 1:12 optical switch 202. OTDR 105 is connected to the input side of the optical switch 202. Under this method, once all the pigtail connectors are connected to their respective optical switch 201, 202, the OTDR test may begin. Once all the pigtails 107, 108 are connected to the optical switches 201, 202 respectively, the optical switches 201, 202 are individually operated to complete the OTDR test on each of the optical fibers. In this example, the OTDR test can be performed on the individual fibers without having to manually attach and then remove each pigtail connector to the OTDRs 101 and 105 one at a time. While this method may be more time efficient in determining the losses at splice point 103 than the method as previously described in conjunction with FIG. 1, it suffers from other drawbacks. For example, the method as described with respect to FIG. 2 is disadvantageous in that the introduction of the optical switches 201, 202, at both ends, causes additional reflections to be seen by the OTDR which results in inaccuracies.
FIG. 3 illustrates yet another conventional method for measuring splice losses and splicer reliability. As illustrated in FIG. 3, a laser 301 is connected to the output side of an 1:12 optical switch 302. The pigtails 107 connected to the first ends of fiber optic cable 102 are connected to the output side of optical switch 302. Similarly, pigtails 108 connected to the first ends of fiber optic cable 104 are connected to an input side of a 12:1 (i.e., for example, 12 inputs and 1 output) optical switch 303. The output end of optical switch 303 is connected to a light meter 305.
To determine true loss at splice point 103 and splicer reliability, using the method illustrated in FIG. 3, it is required that reference measurements be taken at splice points 103 for both cables 102 and 104, prior to any splicing. A reference measurement for cable 102 may be taken by coupling a light meter (not shown) to the second ends of cable 102 (i.e., at splice point 103). This method requires connecting or splicing pigtails (not shown) to the second ends of the optic cable 102 and further coupling each of the pigtail connectors to the optical switch. Reference measurements are taken by the light meter (not shown) at splice point 103 by cycling the optical switch to permit the transmission of light generated by laser 301 through each of the optical fibers. The laser 301 transmits light signal at a predetermined power level and the received power level is measured using a light meter. The above process is repeated to obtain a reference measurement for cable 104 at splice point 103. These reference measurement readings respectively represent the loss of the optical switches, pigtail connectors and splices, and the total loss through each of optical fibers. The reference measurement readings indicating the power loss across each of the optical cables and associated hardware (i.e., pigtails, optical switches, etc.) are recorded and used as a reference to determine the true loss of splice point 103 once optical fibers 102 and 104 have been spliced together.
Referring again to FIG. 3, the conventional method for determining the true loss of the fiber optic splices using lasers and light meters will now be described. In this case, after reference measurements are taken as described above, cables 102 and 104 are be spliced together at splice point 103. It is required that the optical switches 302, 303 be configured to permit the light transmitted by laser 301, on the selected fiber at switch 302, to be received by the light meter 305 on the same optical fiber as selected by switch 303. For example, if the optical switch 302 is set to permit the laser 301 to transmit light on the fourth output of the optical switch 302, then the optical switch 303 must be set to receive the light at the light meter 305 on the fourth input. If the two optical switches are not so coordinated, the proper measurement at light meter 305 will not be measured. The light meter 305 receives the transmitted light signal from laser 301, and a user records the power level received at the light meter 305. Accordingly, the total loss through the cables 102, 104, optical switches 302 and 303, pigtails 107 and 108, and splice point 103 along a single fiber may be determined by subtracting the received power level at light meter 305 from the transmitted power level by laser 301. Finally, the loss of the optical splice at splice point 103 can be determined by subtracting the reference measurements from the total loss. Although this may result in more accurate splice measurements and splicer reliability as compared to those of FIGS. 1 and 2, this method is disadvantageous in that substantial effort and time is required to make individual reference measurements as described above. Attaching pigtails to each of the optical fibers at splice point 103, taking measurements, re-cleaning and re-cleaving the fibers for splicing is extremely labor intensive and time consuming. In addition, if the optical switches are not properly coordinated, improper measurements may occur. Furthermore, optical switches float (i.e., the losses introduced by optical switches may vary over time) making it more difficult to accurately determine the reliability of the optical splicer. Although optical switches having more predictable losses are available, such switches tend to be cost prohibitive for many applications.
Thus, what is needed is a time efficient, cost effective and accurate method for measuring splice losses as well as the reliability of the splicer itself. What is also needed is a fiber optic testing method that provides accurate power loss readings and reduces the need for manual calculations.
In operation, embodiments of the present invention disclose a time, labor and cost efficient system and method for testing the reliability of optical splices. The disclosed embodiments permit rapid and accurate reference measurements for a plurality of optical fibers while minimizing additional equipment and their corresponding losses. Splicing efficiency is also improved since ends of the plurality of optical fibers can be placed in a mass fusion splicer without further cleaving, cleaning or other preparation. Testing efficiency may be further improved by simultaneously transmitting light through more than one optical fiber and mathematically determining the losses on each of the optical fibers. The reliability of the optical splices determined by the disclosed method and system corresponds to the reliability of the optical splicers.
Under embodiments of the present invention, optical fibers are simultaneously connected to the integrating sphere coupled to a light meter. Losses introduced by the additional pigtails and the floating losses of the second optical switch are eliminated. The configuration under the present invention is additionally advantageous since losses can be determined even more efficiently by mathematical calculations and/or coupling the light meter to an intelligent device.
The present invention introduces a system and method for enhanced fiber optic splice measurement and for determining the reliability of fiber optic splicers. In one embodiment, a signal may be transmitted through each of a plurality of optical fibers at one end. At the other end, the plurality of optical fibers may be coupled to an integrating sphere. A light meter may further be coupled to the integrating sphere for measuring the signal quantity received at the integrating sphere. Accordingly, a reference measurement representing the received quantity of signal at the integrating sphere may be determined in an efficient manner without removing and attaching each of the fibers from the light meter. In embodiments of the present invention, the second ends of the plurality of optical fibers may be coupled to a fiber holder. The fiber holder may be coupled to the integrating sphere either directly or via an adapter. In any event, a first reference measurement reading at the integrating sphere may be taken according to embodiments of the present invention.
In alternative embodiments of the present invention, first ends of the plurality of optical fibers may be connected to an optical switch. The optical switch may permit transmission of an optical signal through each of the plurality of optical fibers to the integrating sphere. In embodiments of the present invention, the optical switch may be switched manually or automatically without user intervention. In embodiments of the present invention, the light meter may record the signal level received at the integrating sphere and based on the transmitted signal level, automatically calculate a loss for each of the individual fibers. In embodiments of the present invention, the light signal may be transmitted through more than one optical fiber simultaneously and the reference measurements and/or losses through each may be mathematically calculated or interpolated using known techniques. In yet alternative embodiments of the present invention, the light meter, for example, may automatically indicate whether the calculated loss for the individual fibers is within an acceptable range.
Embodiments of the present invention further introduce an efficient method for measuring signal losses through optical fibers including a splice point and for determining the reliability of a fiber optic splicer. In one example, the fiber holder having a plurality of optical fibers may be removed from the integrating sphere and placed in a mass splice optical fiber splicer. A second holder having first ends of optical fibers from a second cable may further be placed in the mass fiber splicer for splicing with the first cable. Accordingly, the optical fibers in the first fiber holder may be spliced with the optical fibers in the second fiber holder utilizing the mass splicer. In embodiments of the present invention, second ends of the second fiber optic cable may be coupled to a second fiber holder. The second fiber holder may be coupled to the integrating sphere coupled to a light meter for measuring received signal at the integrating sphere. Accordingly, a second reference measurement reading may be taken at the integrating sphere. By taking the difference between the first reference measurement reading and the second reference measurement reading, a true loss at the splice point as well as the reliability of the fiber optic splicer may be determined.
Although the invention has been defined using the appended claims, these claims are exemplary and limiting to the extent that the invention is meant to include one or more elements from the system and methods described herein. Accordingly, there are any number of alternative combinations for defining the invention, which incorporate one or more elements from the specification (including the drawings, and claims) in any combinations or subcombinations.